Piston construction



June 25, 1963 Filed Oct. 25, 1961 O.KAUP

PISTON CONSTRUCTION 2 Sheets-Sheet 1 m venzor OTMAR KA UP June 25, 1963 o. KAUP 3,095,221

, PISTON CONSTRUCTION Filed Oct. 25, 1961 2 Sheets-Sheet 2 INVENTOR 07' MAR KAUP BYWMM/W ATTORNEY5 United States Patent 3,095,221 PISTON CGNTRUCTIGN Gtmar Kaup, Aschaifenburg, Germany, assignor to Gesellschaft fur Lindes Eismascninen Aktiengesellschaft,

Wiesbaden, Germany Filed Oct. 25, 1961, Ser. No. 147,604 Claims priority, application Germany Nov. 2, 1966 6 Claims. (Cl. 287-21) The present invention relates to a piston which is particularly adapted for a swash-plate axial piston unit such as a pump, more particularly, to the provision of a resilient member in said piston to equalize the lateral forces exerted by the connecting rods against the pistons and accordingly against the cylinder walls.

The conventional axial-piston unit as involved in this invention comprises a swash-plate axial-piston pump or a wobble-plate engine. The present invention can best be understood when described in connection with the so-called swash-plate or wobble-plate engine.

This type of engine essentially comprises a cylinder barrel having an odd number of cylinders which are arranged in the cylinder barrel in the form of a circle with the axes of the cylinders being parallel. The pistons within the cylinders are connected by ballheaded connecting rods to a socket ring. The socket ring is rotatably mounted about its central axis. The socket ring may be tilted to an angle with respect to the central axis of the cylinder barrel. Thus, the axis of the socket ring will form an acute angle with the axis of the cylinder barrel when the socket ring is in its operating position.

One end of each connecting rod is fastened by a ball and socket connection to the piston and the other end by a ball and socket connection to the socket ring. The plane in which the ring socket ends of the connecting rods are guided is inclined with respect to the longitudinal axis of the cylinder barrel.

When such an engine is being operated, the explosions in each cylinder force the respective pistons from out of the cylinder. Since the end of the connecting rod is supported on an inclined plane, as provided by the socket ring, the ring end of the connecting rod will move along this inclined plane until the piston has been displaced its maximum distance within the cylinder and the connecting rod socket end is at its maximum distance from the cylinder head. The cylinder barrel rotates to follow this movement of the connecting rod. Accordingly, in the operation of such an engine, when the socket ring end of the connecting rod first begins to move along the inclined socket ring plane, the connecting rod will first be tilted as far as possible and then the cylinder barrel will be rotated about its longitudinal axis to permit the socket end of the connecting rod to travel to its maximum position on the inclined plane.

The piston ends of the connecting rods will always move on a cylindrical surface whose longitudinal axis is identical with that of the cylinder barrel. The diameter of this cylindrical surface is determined by the arrangement of the cylinders in the cylinder barrel.

The path of movement of the socket ring ends of the connecting rods defines a circle but one whose rotational axis is inclined with respect to the axis of the cylinder barrel. The projection of the circle onto a plane which is perpendicular to the longitudinal axis of the cylinder barrel would produce an ellipse. As previously pointed out, the projection of the paths of the piston ends of the connecting rods onto the plane which is perpendicular to the longitudinal axis of the cylinder barrel would produce a circle.

When a piston is positioned in one of its dead center positions, the socket ring end of its connecting rod "ice will be positioned at the intersection of the projected ellipse with the minor axis of this ellipse. In this position the connecting rod is inclined with respect to the major axis of the ellipse. The major axis of the ellipse also represents the intersection of a plane which is perpendicular to the longitudinal axis of the cylinder drum with the inclined plane of the socket ring.

In order to limit the inclination of the connecting rod when its piston is in the dead center position, the distance between the socket ring end of the connecting rod and the rotational axis of the socket ring must be greater than the radius of the above-mentioned cylindrical surface. As a result, the circle through which the socket ring ends of the connecting rods move has a greater diameter than the circle through which the piston ends of the connecting rods are guided. The difierence between the diameters of these two circles is so chosen, that the inclination of a connecting rod with respect to the central longitudinal axis of the ellipse, when its corresponding piston is in a dead center position, is at least approximately equal to the inclination of this connecting rod in the opposite direction when the socket ring end of the connecting rod is positioned at the in- .tersection of the ellipse with the major axis thereof. In general, this angle of inclination is from 1 to 2.

The connecting rod will have its greatest inclination or slope with respect to the longitudinal axis of the cylinder barrel when its socket ring end will have moved from the dead center position by an angle of 45. In this position the connecting rod in previously known axial piston units will engage the inner surface of the piston skirt. Thereby a force is transmitted from the connecting rod to the piston and from the piston to the cylinder barrel. This force effects the rotation of the cylinder barrel about its longitudinal axis.

Because of the inclination of the connecting rod irrespective of its contact with the interior surface of the piston skirt, a lateral force is produced which is at right angles to the axis of the cylinder barrel. This lateral force is a component of the force created by the pressure exerted by the expanding gases in the cylinder on the piston. This component force P can be represented by the following relationship:

P =P- sin ,8

wherein P is the force acting on the piston and exerted along the connecting rod and [3 is the angle between the longitudinal axis of the connecting rod and the axis of the cylinder. Therefore, in order to rotate the cylinder barrel, not only must the friction between the cylinder barrel and its mounting thereof be overcome, but also the sum of the above-mentioned component forces which are opposite to the direction of rotation of the cylinder barrel.

In the conventional axial piston unit the force necessary for rotating the cylinder barrel is obtained by one connecting rod contacting the inner surface of its respective piston skirt. In an axial piston unit having an odd number of cylinders the connecting rod which transmits the peripheral force to rotate the cylinder barrel alternates between that connecting rod which is just being positioned on the pressure side and that connecting rod which is just being positioned on the low-pressure or suction portion of the cycle for the piston. Because of the relatively high speed at which the cylinder barrel rotates, the rapid sequence of sounds formed by the contact of the connecting rods With the piston skirts produces a very loud and disturbing noise. The acoustic frequency of this sound is equal to the product of the revolutions of the cylinder barrel and twice the number of connecting rods since at each rotation of the cylinder barrel each connecting rod will successively twice engage its respective piston skirt. In view of the odd number of cylinders and therefore the connecting rods, it is apparent that the connecting rods do not simultaneously contact the respective piston skirts at each of the four points of intersection of the ellipse with its major and minor axes.

It is therefore the principal object of the present invention to provide a piston for an axial piston unit which eliminates the objectionable noises caused by the engagement of the connecting rods with the piston skirts.

It is a further object of this invention to provide a piston for an axial piston unit wherein, instead of only one connecting rod applying the force to rotate the cylinder barrel, all of the connecting rods contribute in varying degrees dependent upon theirposilrion to the total force for rotating the cylinder barrel.

The objects of the present invention are attained by coating at least that portion of the connecting rod which is positioned within the piston skirt and/or the interior surface of the piston skirt with an elastic resilient material. Since the connecting rods have relatively short horizontal movements with respect to the axis of the cylinder barrel, the several connecting rods will transmit a peripheral force to the cylinder drum wherein the force transmitted by each individual connecting rod depends on the extent to which the resilient material of that connecting rod is deformed by the inclination of the connecting rod. Since a plurality of peripheral forces are applied, the shock-like impacts of single connecting rods against the piston skirts are eliminated and the metallic sounds are prevented.

As a modification of this invention the entire space within the skirt of a piston between the connecting rod and the inner surface of the piston skirt can be filled with a resilient material. Accordingly, those connecting rods which at any one time are inclined a relatively small angle from the axis of the cylinder, will transmit some peripheral force onto the piston. This arrangement simultaneously reduces the component forces which are transmitted from a wall of the piston to the cylinder wall and accordingly skin friction in the cylinder is reduced.

A further modification of this invention comprises securing the elastic or resilient material to the inner surface of the piston skirt and the connecting rod.

Other objects and advantages of this invention will be apparent upon reference to the accompanying description when taken in conjunction with the following drawings, wherein:

FIGURE 1 is a longitudinal sectional view of a piston and connecting rod embodying the present invention; and

FIGURE 2 is a view similar to that of FIGURE 1 but showing a modification of the invention.

FIGURE 3 is a view similar to that of FIGURE 2, but showing a still further modification of the invention.

Returning now to the drawings, wherein like reference symbols indicate the same parts throughout the various views, with particular reference to FIGURE 1 there is shown a piston *1. The piston 1 is connected to its respective connecting rod 2 by a ball end 3. There is an axial passage 4' in the end of the piston which provides a source of lubrication for theball end 3.

The other end of the connecting rod comprises the socket end which has also a ball 5 which is connected to a socket ring 6 by means of a fastening ring 7, which is retained in place by a retaining ring 8.

Depending from the lower end of the piston 1 and integral therewith is a piston skirt portion 9. Rubber or some other suitable resilient and elastic material is positioned between the skirt 9 of the piston and the connecting rod 2, as shown at 10.

The rubber 10 is vulcanized to both the inner surface of the skirt 9 and the outer surface of the connecting rod shank which, as can be seen in FIGURE 1, has its major portion enclosed within the skirt 9. Because of this tight connection between the rubber, the connecting rod and the piston skirt, not only will compression forces be transmitted to the piston where the connecting rod approaches the inner surface of the piston skirt, but also tension forces where the connecting rod moves away from the piston skirt portion 9.

There are several other structures by which the resilient material may be mounted within the piston skirt. The rubber sleeve 10 may be introduced into the piston skirt and then secured in place by means of a flange or collar mounted on the lower end of the inner surface of the skirt. In addition, an annular groove could be cut in the lower end of the skirt and a split retainer ring inserted therein to hold the resilient material in position. The rubber sleeve or resilient material can be secured within the piston skirt so as to'tightly retain the piston ball end 3 of the connecting rod in locking engagement with the piston. As a result, locking rings and grooves for securing the ball end 3 in the piston may be eliminated.

As seen in FIGURE 1, the resilient material virtually fills the space in the skirt portion between the connecting rod and the inner surface of the skirt. However, the results of this invention can also be obtained by merely applying a layer of the resilient material tothe inner surface of the skirt portion and to the shank of the connecting rod enclosed within the skirt portion.

As can be seen in FIGURE Lthe longitudinal axis of the piston is indicated at 11 and the longitudinal axis of the connecting rod is indicated at 12. The connecting rod is illustrated in an inclined position so that an angle is formed between the two axes 11 and 12. As a result, the elastic material is compressed on the left-hand side of the connecting rod and is placed in tension on the righthand side of the connecting rod. These tension and compression forces contribute to the-peripheral force necessary for rotating the cylinder barrel.

Proceeding next to FIGURE 2, the piston 1 is shown having a connecting rod 2 the ball end 13 of which is secured in the piston 1. An annular groove 14 is provided in the upper end of the skirt portion 9 and a locking ring 15 is positioned in the groove to lock the ball end 13 in position and thereby prevent the withdrawal of the connecting rod 22 from the piston 1.

The shank of the connecting rod 22 is provided with a reduced diameter portion 16 with the elastic material 19 being positioned between the shank portion 16 and the skirt 9. The lower end of the shank of the connecting rod is provided with an increased diameter portion 17 at that area of the shank where the connecting rod engages the skirt 9. The lower end of the inner surface of the skirt 9 is bevelled so as to have a conical surface as indicated at 18. The angle of this conical surface is so chosen that when the shank portion 17' engages the conical surface, a linear contact will occur between the conical surface 18 and the shank portion 17. The engagement of the enlarged diameter portion 17 of the connecting rod with the conical surface 18 on the piston skirt limits the compression of the elastic material 10 to an unreasonably high degree.

Since the connecting rod portion '17 is not covered with elastic material, a metal-to-metal contact between the connecting rod portion 17 and the skirt 9 will occur. Therefore, this modification as illustrated in FIGURE 2 is desirable when the force to be transmitted between the connecting rod and the piston is of such a high value, that the elastic material may be compressed or distorted beyond its limits and therefore damaged.

FIGURE 3 difiers from FIGURE 2 by the provision of an inner flange 23 on the lower end of the inner surface of the skirt portion.

Thus it can be seen that the present invention provides an improved piston which is particularly adapted for axial piston units such as swash-plate pumps or wobble-plate engines.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions and, accordingly, it is desired to comprehend such modifications within this invention as may fall Within the scope of the appended claims.

What is claimed as this invention is:

1. A piston particularly adapted for a swash-plate axial-piston unit, and comprising a piston body having a depending skirt portion on one end thereof, a connecting rod pivotally connected to said one end of said piston body with a major portion of said rod extending Within said skirt portion, and a layer of resilient material on the portion of the connecting rod Within said skirt portion and the inner surface of said skirt portion.

2. A piston particularly adapted for a swash-plate axialpiston unit, and comprising a piston body having a depending skirt portion on one end thereof, a connecting rod pivotally connected to said one end of said piston body with a major portion of said rod extending within said skirt portion, and a resilient material member substantially occupying the space in said piston between the inner surface of said skirt portion and said connecting rod.

3. A piston particularly adapted for a swash-plate axial-piston unit, and comprising a piston body having a skirt portion depending from one end thereof, arr inner flange on the lower end of the inner surface of said skirt portion, a connecting rod pivotally connected to one end of said skirt body with a major portion of said rod extendin within said skirt portion, and a resilient material member substantially occupying the space in said piston between the inner surface of said skirt portion and said connecting rod and secured in position by said flange 4. A piston particularly adapted for a swash-plate axial-piston unit, and comprising a piston body having a depending skirt portion on one end thereof, a connecting rod pivotally connected to said one end of said piston body with a major portion of said rod extending within said skirt portion, and a resilient material member substantially occupying the space in said piston between the inner surface of said skirt portion and said connecting rod, said resilient material being fastened to one of said connecting rod and the inner surface of said skirt portion.

5. A piston particularly adapted for a swashplate axial-piston unit, and comprising a piston body having a depending skirt portion on one end thereof, a connecting rod pivotally connected to said one end of said piston body with a major portion of said rod extending within said skirt portion, and a resilient material member substantially occupying the space in said piston between the inner surface of said skirt portion and said connecting rod, said resilient material being fastened to both said connecting rod and the inner surface of said skirt portion. 6. A piston particularly adapted for a swash-plate axial-piston unit, and comprising a piston body having a depending skirt portion on one end thereof, a connecting rod pivotally connected to said one end of said piston body with a major portion of said rod extending within said skirt portion, said connecting rod having an enlarged portion on the shank thereof and engageabie with said skirt portion, and a resilient material member substantially occupying the space in said piston between the inner surface of said skirt portion and said connecting rod above said enlarged portion whereby said enlarged portion is not covered by said resilient material.

References Cited in the file of this patent UNITED STATES PATENTS 891,993 Hess June 30, 1908 1,996,826 ()hmart Apr. 9, 1935 2,436,908 Weenen et al. Mar. 2, 1948 2,569,669 Doeg Mar. 14, 1950 2,847,261 Cornelius Aug. 12, 1958 2,856,250 Thoma Oct. 14, 1958 2,889,042 Budzich Mar. 31, 1959 

1. A PISTON PARTICULARLY ADAPTED FOR A SWASH-PLATE AXIAL-PISTON UNIT, AND COMPRISING A PISTON BODY HAVING A DEPENDING SKIRT PORTION ON ONE END THEREOF, A CONNECTING ROD PIVOTALLY CONNECTED TO SAID ONE END OF SAID PISTON BODY WITH A MAJOR PORTION OF SAID ROD EXTENDING WITHIN SAID SKIRT PORTION, AND A LAYER OF RESILIENT MATERIAL ON THE PORTION OF THE CONNECTING ROD WITHIN SAID SKIRT PORTION AND THE INNER SURFACE OF SAID SKIRT PORTION. 